The collet used to secure the work in an automatic bar machine, screw machine, or the like, is normally closed by shifting an outer spindle over an enlarged forward end portion of the collet. The means for shifting the outer spindle is generally referred to as the "collet closing mechanism", and for many years the most widely used mechanisms of this sort comprised an arrangement of chuck levers mounted in a chuck lever fulcrum. Due, however, to the necessary construction of the parts and their constant subjection to forces of relatively large magnitude, breakage has been common, with attendant risk to personnel and damage to machinery.
Other designs for collet closing mechanisms have been proposed in an effort to avoid such problems, notable amongst which is the so-called "ball-chucker" system. This device utilizes a circular array of ball bearings, which are held within a cage in place behind a slidably mounted thrust collar, and which can be forced by an outer, slidably mounted sleeve into a circumferential channel defined behind the collar. Movement of the sleeve over the ball bearings forces them into the tapered groove, causing the thrust collar to shift forwardly; this motion is transmitted by appropriate means to the outer spindle which, in turn, closes the collet in the usual manner. While such devices offer decided advantages over the earlier lever-operated mechanisms, still they suffer from serious deficiencies. In particular, due to the minimal contact area provided by the spherical bearings, wear on the mating parts is extreme, thus limiting the useful life and practical value of the device.
Accordingly, it is an object of the present invention to provide a novel collet-operating mechanism which avoids the disadvantages of the devices heretofor utilized for the purpose.
It is a more specific object of the invention to provide such a mechanism in which levers are not employed, thus avoiding the risks attendant to the relatively weak construction that such a design entails.
Another more specific object of the invention is to provide such a mechanism in which the rate of wear is reduced substantially from that which is inherent in the use of spherical members for the transmission of closing force, and which therefore affords a much longer useful life.
Yet another object of the invention is to provide such a mechanism which is relatively simple in design and inexpensive to produce, and which nevertheless operates smoothly to provide a positive and dependable closing action.